Diffractive microstructures may be attached to products e.g. for the visual effect given by them, or for authenticating the product.
Diffractive microstructures may be produced e.g. by embossing the surface layer of a substrate coated with a suitable lacquer. The coated substrate is pressed between an embossing member and a backing member in the embossing process. The surface of the embossing member comprises microgrooves, which correspond to the microstructure to be produced. The backing member supports the substrate from the back side during the embossing process such that a sufficient pressure, the embossing pressure, may be directed to the surface layer of the substrate in order to shape the surface to correspond to the microgrooves of the embossing member. It is advantageous for the shaping of the surface of the substrate if the surface layer is plasticized by heating. The temperature of the surface of the substrate during the embossing process is herein called the embossing temperature.
U.S. Pat. No. 4,913,858 discloses a method for producing a diffractive microstructure on the surface layer of a paper coated with a thermoplastic material. The microstructure is formed to the coating by means of a heated embossing roll.
According to the prior art solutions, the diffractive microstructure giving the visual effect is produced in such a way that it corresponds to the microgrooves on the surface of the embossing member, as well as possible.